This invention relates to rotary peristaltic pumps, suitable for miniaturisation, the pump of the invention having a high degree of efficiency and accuracy, making it particularly suitable for medical drugs administration. For example, the pump of the invention is especially suitable for the infusion of insulin or other drugs into ambulant patients, and by reason of its preferred materials of construction as hereinafter described, the pump of the invention is also suitable for use in corrosive environments. However, such uses are merely illustrative and non-limitative.
Previous constructions of rotary peristaltic pumps for medical drug administration have suffered from one or more disadvantages, namely, (a) excessive size and complexity; (b) dependence upon very close tolerances in components subject to wear or warping; (c) susceptibility to the presence of dirt and corrosion; (d) inability to tolerate high temperatures, e.g. sterilisation; (e) high frictional losses and power requirements; (f) excessive wear of pump-tubing; and (g) poorly reproducible delivery volumes or rates.
Thus, previous rotary peristaltic pumps have been constructed with compression rollers held in a cage by bearing pins. The driving force is transmitted either via a cage which is mounted on the driving shaft (hereinafter referred to a rotary peristaltic pump "Type A"), or via a central shaft or roller whose rotation is transmitted to the compression rollers by direct contact, so that the cage travels more slowly than the driving shaft (hereinafter referred to as rotary peristaltic "Type B").
Rotary peristaltic pump "Type A" requires rigid bearing pins to secure the compression rollers to the cage and these bearings are susceptible to wear and seizing. Wear results in failure adequately to compress the tubing, resulting in loss of accuracy and pump failure. Seizing results in erratic operation and excessive wear of pump tubing.
Two modifications of rotary peristaltic pump "Type A" exist, which seek to overcome the problems occasioned by wear, namely, (1) omission of the outer race, which is identified as the `Holter` pump, the tubing merely being stretched over the rollers, resulting in an extremely pulsatile flow with considerable flow reversal, moreover, the pump can only maintain constant mean flow rates at low inlet and outlet pressures, and (iii) spring mounting of the rollers or of a segment of the outer race, which is more satisfactory in operation but is complex and often bulky.
Rotary peristaltic pump "Type B" is not dependent on a rigid cage and close tolerance bearing between the cage and the compression rollers. However, the cage generally requires a separate central bearing and this is very sensitive to the least unevenness in the roller from wear or the presence of dirt, which rapidly results in erratic operation, heavy wear and consequent pump failure, this problem being exacerbated by miniaturisation.
The rotary peristaltic pump of the present invention avoids many of the above problems, in particular, by being compact and eminently suitable for miniaturisation; by having very low power requirements; by being of considerably simpler construction and thus easy to manufacture; by being less susceptible to failure through wear or seizing; by being capable of great accuracy, especially at low flow rates; and by not requiring lubrication due to selection of the materials of construction.